Fuse having an improved sheathing



May 14, 1968 J. PRIOR ET AL 3,382,802

FUSE HAVING AN IMPROVED SHEATHING Filed Jan. 10, 1966 OUTER SHELL (THERMOPLASTIC 3-FIBROUS TUBE) MATERIAL 5 IS QW 4-WlRE-TYPE EXPLOSIVE 2" FIBROUS MATERIAL MATERIAL INVENTORS JOSEF PRIOR HILDEBERT WUCKEL ALOYS FLORIN BY e ATTORNEYS United States Patent 3,382,802 FUSE HAVING AN IMPROVED SHEATHENG Josef Prior, Troisdorf, Cologne, and Hildebert l/Vuclrel and Aloys Florin, Spich, Cologne, Germany, assignors to Dynamit Nobel Akfiengesellschaft, Troisdorf, Germay Filed Jan. 10, 1966, Ser. No. 519,467 Claims priority, application Germany, Jan. 19, 1965,

8 Claims. Cl. 102-27 ABSTRACT OF THE DESCLOSURE This invention relates to fuses. More particularly, it relates to fuses having a new and improved sheathing or casing. Even more particularly, the invention relates to fuses having a sheathing or casing made from strands or threads of thermoplastic material or a ductile metal or from filaments or bands of thermoplastic material or glass.

It is well known in the art that fuses serve to transmit detonations to distantly located systems which are adapted to be detonated. Such fuses comprise a casing or sheathing, the so-called enclosure, having a continuous explosive core for propagating the initial impulse, wherein the correspondin velocity of propagation of the initial impulse depends upon the kind of explosive being used and the concentration thereof. The type and construction of the enclosure are of decisive significance in obtaining an advantageous utilization of the properties of the explosive. For example, if, in an effort to manage with as small a quantity of explosive as possible, the quantity thereof employed is less than the socalled critical diameter of an explosive column for a given explosive without an enclosure, at which critical diameter the explosive essentially detonates completely, the danger of the ignition of the detonation may be effectively counteracted by selecting a correspondingly strong enclosure. However, significant difficulties in the choice and construction of a suitable enclosure therefor result from the fact that different conditions must be taken into account for practically every explosive.

Trinitrotoluene (TNT) was initially employed as the explosive in fuses, and a lead tube served therein as the enclosure. In preparing such a fuse, the lead tube was filled with the explosive and the tube, initially having a relatively large diameter, was successively drawn through a number of extruder nozzles having progressively smaller inside cross-sections until finally, at a corresponding elongation of the tube, the desired small diameter of the fuse was attained.

However, the metal enclosures were uneconomical and had various important disadvantages, such as, for ex ample, great weight and brittleness which led to easy breakage at low temperatures and which only permitted a discontinuous preparation of fuses having certain lengths. When desensitized mercuric fulminate was employed as the explosive, and particularly after the advent of pentaerythritol tetranitrate, it became possible to depart from the metal enclosures having the above-mentioned disadvantages and to cover or braid the powdery explosive core with textile fibers. This is done by introducing or transferring the explosive from a filling funnel into a thin band or ribbon made of paper, a synthetic material or an otherwise suitable material, the band being continuously wound or wrapped at the lower end thereof in a spiraling and overlapping fashion. The band filled with explosive is then either spirally wound or braided with several layers of textile filaments twisted from fibers. Depending upon the particular requirement therefor, and particularly as a protection against moisture, the fuse thus obtained may be additionally provided with a coating of lacquer, thermoplastic material or the like and, as a protection against mechanical damage, with a wide-mesh covering or braiding made from metal strands.

Recently, fuses having considerably reduced explosive contents have been greatly developed. The reduction in the quantity of explosive employed has become possible either by returning to the old principle of having the explosive surrounded or enclosed with a ductile metal or by enclosing the explosive with a compact sheathing made from a thermoplastic material. While, in the first instance, theaforementioned disadvantages and drawbacks must again be accepted as a logical consequence, the latter embodiment of having a compact sheathing made from a thermoplastic material involves considerable danger, particularly when making the explosive fuses. This danger results from the fact that the explosive is introduced directly behind an annular nozzle into the still hot synthetic plastic tube which is continuously being extruded therefrom.

One of the objects of the present invention is to provide an improved fuse which does not have the disadvantages and deficiencies inherent in the prior art fuses as mentioned hereina-bove.

Another object of the present invention is to provide an improved fuse which has a reduced explosive content but, at the same time, does not present a danger of premature explosion.

A further object of the invention is to provide an improved fuse having a casing or sheathing which may be made efficaciously and economically.

A still further object of the invention is to provide an improved fuse having a reduced explosive content which may be prepared in a continuous manner efiicaciously.

Yet another object of the present invention is to progi-de an improved fuse which is light in weight and dura- These and other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following specification and claims.

In accordance with the present invention, fuses having a reduced explosive content which detonate faultlessly and completely may be obtained if the sheathing or casing therefor is made from strands or threads of thermoplastic material and/or a ductile metal or from filaments or hands of a thermoplastic material and/or glass made from fibers or threads thereof. Thus, instead of employing textile filaments which have the aforementioned disadvantages and drawbacks, the present invention involves adhering to the old proven principle but also without the disadvantages and drawbacks thereof, such as were encountered with the old solid metal casings.

In the attached drawing, the single figure is an elevational view, partially broken away, of an exemplary fuse in accordance with the present invention.

Referring now to said drawing, the invention is illustrated as a fuse broadly comprising an explosive core 6 enveloped first by a strip 5 of paper, synthetic resinous material or the like, rolled in the shape of a tube at right angles to its longitudinal extension. The strip 5 is followed by the wire-like material 4 of metal or plastic,

3 wound in a spiral manner, the fibrous material 3, the fibrous material 2, for example, of glass or plastic, and, finally, by an outer shell or sheathing It in the form of a tube made of, for example, a thermoplastic resin.

By fuses having a reduced explosive content is meant, for example, fuses having an amount of explosive of 7 grams per meter and less. In fact, the quantity of explosive may be more greatly reduced, the greater the proportionate amount of thermoplastic or n etal threads or strands or glass fibers employed in the enclosure. Thus, it is possible, for example, when using a sheathing consisting entirely of metal strands or wires or of glass fiber filaments or bands, to reduce the explosive quantity to 0.8 gram per meter without jeopardizing or hindering the operation and function of the fuse.

Suitable filler materials for the fuses herein include all of the primary explosives and igniting agents having a reaction zone length of less than 0.5 mm. Thus, for example, substances such as lead azide, diazodinitrophenol, lead salts of the nitrophenols and lead triethanolaminoperchlorate, as well as all the solid nitric acid esters which have a detonation sensitivity either equal to or greater than that of nitropentaerythritol, and nitroamines having a sensitivity to detonation which is either equal to or greater than that of trimethylenetrinitroamine (T may be employed.

According to a further embodiment of the present invention, it has also been found that for the safe operation of a fuse, particularly one having a reduced amount of explosive, the explosive particles should have a size such that they will pass through a strainer having an inside width mesh of 100 and wherein at least half of the particles of explosive will also pass through a strainer having an inside width mesh of 50 This embodiment is of particular importance in the preparation of fuses having a very low explosive content of, for example, 1 or 2 grams per meter, since the particle sizes obtained by this straining process guarantee a safe propagation of the detonation in fuses having an explosive core with a very small diameter. In principle, however, this embodiment may also be advantageously utilized in fuses of any desired type, such as those having a relatively large explosive content of, for example, 7 grams per meter or more.

The thermoplastic material which may be employed in the present invention includes any of the synthetic resins that may be softened by heat which regain their natural properties upon cooling. Such resins are well known in the art and include, for example, polyvinyl chloride, copolymers of vinyl chloride with vinyl acetate( particularly containing from 2 to vinyl acetate) and/or styrene, polyethylene, polypropylene, copolymers of ethylene and propylene and polymers and copolymcrs of styrene and of the arcylates and methacrylates. These resins are described in, for example. Modern Plastics Encyclopedia, Issue for 1963, volume 40, No. 1A, Sept. 2, 1962. The particular thermoplastic resin employed is not critical and may be chosen as desired.

As is known in the art, a ductile metal is one that may be lengthened or flattened out without losing continuity when subjected to tensile stresses or rolling. Examples .4}. thereof which may be employed in the present invention include bronze, copper, lead and pure iron.

The manufacture of the fuse sheathing according to the present invention may be carried out by known techniques but the most preferred method therefor is by spinning.

The term threads or thread-like elements as used herein includes suitably processed fibers, wires and single continuous filaments as Well as mutifilaments of such elements formed into bands, strands or the like.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications are intended to be included within the scope of the following claims.

We claim:

it. A fuse comprising an explosive core encased by a sheathing, said fuse having, at the most, an amount of explosive of 7 grams per meter, said explosive having a reaction zone length of less than 0.5 mm., and said sheathing consisting essentially of spun thread-like elements of a material selected from the group consisting of ductile metals and polymers and copolymers of vinyl chloride, vinyl acetate, styrene, ethylene, propylene, the acrylates and the methacrylates.

2. The fuse according to claim ll, wherein the ductile metal is bronze.

3. The fuse according to claim 1, wherein at least half of the particles of explosive have a maximum particle size Of M.

4. The fuse according to claim ll, wherein said sheathing comprises bands of said polymers and copolymers made from said thread-like elements thereof.

5. The fuse according to claim 11, wherein the particles of explosive have a maximum particle size of 100,.

6. The fuse according to claim 5, wherein the amount of explosive in said fuse is l to 2 grams per meter and wherein at least half of the particles of explosive have a maximum particle size of 5011..

7. The fuse according to claim 1, wherein said spun thread-like material is a thermoplastic resin selected from the group consisting of polymers and copolymers of vinyl chloride, vinyl acetate, styrene, ethylene, propylene, the acrylates and the methacrylates.

8. The fuse according to claim 1, wherein said spun thread-like material is a ductile metal selected from the group consisting of bronze, copper, lead and iron.

References Cited UNITED STATES PATENTS 2,445,032 7/ 1948 McFarland 102-27 2,982,210 5/1961 Andrew et al. 102-27 2,992,087 7/1961 Fassnacht et a1 149-111 3,155,038 11/1964 Smith 102-27 3,260,201 7/1966 Kelly et a1. 102-27 BENJAMIN A. BORCHELT, Primary Examiner. V. R. PENDEGRASS, Assistant Examiner. 

